The disclosure of Japanese Patent Application No. 2000-297404 filed on Sep. 28, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates generally to a damping actuator applicable to an active vibration-damping device attached to a subject member for exhibiting an active damping effect with respect to vibrations excited in the subject member, and such an active vibration-damping device equipped with the damping actuator. In particular, the invention is concerned with a damping actuator suitably usable in a vibration-damping device for an automotive vehicle, such as an engine mount, a body mount and a vibration damper, and an active vibration-damping device equipped with such a damping actuator.
2. Description of the Related Art
For damping or reducing a vibration of a subject member or a member of a vibration transmitting system, there have been generally used vibration damping means which utilize a damping effect exhibited by a shock absorber or an elastic body member, or vibration isolating or insulating means which utilize a spring effect exhibited by a coil spring or an elastic body member. These vibration-damping devices are all adapted to provide a passive vibration damping or isolating effect, and are not capable of sufficiently damping or isolating a vibration whose characteristics tend to vary. In the light of this drawback of the known vibration device, there have been developed active vibration damping devices adapted to apply an oscillating force to the subject member for actively or positively offsetting or attenuating vibrations to be damped. Known examples of such active vibration damping devices are disclosed in JP-A-11-351322 and JP-A-2000-35083.
The active vibration-damping device requires a damping actuator for generating the oscillating force. Such a damping actuator is required to be capable of accurately controlling a frequency of the oscillating force. To meet this requirement, a known damping actuator, which has been suitably used in the active vibration damping devices as disclosed in the above-indicated publications, includes: an inner shaft member and an outer sleeve member disposed radially outwardly of said inner shaft member with a radial spacing therebetween; a permanent magnet fixed to the inner shaft member; and a coil fixed to the outer sleeve member. Upon energization of the coil, magnetic poles or fields are given on the side of the outer sleeve member and act on magnetic poles or fields given on the side of the inner shaft member owing to the permanent magnet, to thereby generate an oscillating force which causes a relative movement of the inner shaft member and the outer sleeve member in an axial direction of the inner shaft member. In the known damping actuator, therefore, an electric current applied to the coil is regulated so as to control generated electromagnetic force or magnetic force functioning as the oscillating force.
In particular, when the active vibration-damping device is used for damping vibrations excited in an automotive vehicle, the damping actuator is further required to generate a sufficiently large oscillating force with a reduced power consumption, as well as to be compact and lightweight.
However, the known damping actuator is insufficient to meet the above-mentioned requirements. Thus, the known damping actuator has been desired to be improved in all of the above-mentioned requirements, namely to be more (i) compact in size, (ii) light in weight, and (iii) efficient in generating the oscillating force in terms of power consumption.
It is therefore a first object of this invention to provide a novel damping actuator which is simple in construction and reduced in size and weight, and which is capable of generating an oscillating force with improved efficiency in terms of a required amount of electric power consumption.
It is a second object of this invention to provide an active vibration-damping device which is equipped with the damping actuator according to the present invention.
The first object may be attained according to the following modes (1)-(7) of the invention, and the second object may be attained according to the following modes (8)-(11) of the invention, each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the present invention is not limited to the following modes or combinations of technical features, but may otherwise be recognized based on the thought of the present invention that described in the whole specification and drawings or that may be recognized by those skilled in the art in the light of the disclosure in the whole specification and drawings.
(1) A damping actuator comprising: (a) an inner shaft member; (b) an outer sleeve member disposed coaxially with and radially outwardly of the inner shaft member with a radial spacing therebetween such that the outer sleeve member being movable relative to the inner shaft member; (c) a coil disposed coaxially with and fixedly mounted on the inner shaft member; (d) an inner yoke fixedly disposed on the coil so as to form at an outer circumferential portion thereof a plurality of inner magnetic pole portions located in axially opposite sides of the coil, the plurality of inner magnetic pole portions being given magnetic poles upon energization of the coil; (e) a permanent magnet disposed radially outwardly of said coil and/or said inner yoke with a radial spacing therebetween and fixedly mounted in the outer sleeve member in a coaxial relation with each other so as to extend in a circumferential direction of the outer sleeve member; and (f) an outer yoke fixedly disposed on the permanent magnet and associated with the permanent magnet to form a plurality of outer magnetic pole portions, the plurality of outer magnetic pole portions being given magnetic poles by the permanent magnet, the inner magnetic pole portions and the outer magnetic pole portions are opposed to each other in a radial direction perpendicular to an axial direction of the inner shaft member with a predetermined radial gap therebetween, and are offset from each other in the axial direction, while the coil is in a non-energized state, the coil being energized for generating a magnetic axial driving force acting between the inner and outer magnetic pole portions so that the inner and outer magnetic pole portions are moved relative to each other in the axial direction.
In the damping actuator constructed according to the first mode (1) of this invention described above, the coil is fixed to the inner shaft member, unlike the conventional damping actuator in which the coil is fixed to the outer sleeve member. In this arrangement, a diameter of the coil is made small, whereby a length of a wire winding around the coil is made small to the number of winding of the coil. Since a resistance value of the wire to flow of an electric current therethrough is made small in proportion as the length of the wire is reduced, an amount of electric power consumption of the damping actuator can be reduced. Likewise, the weight of the damping actuator is made small in proportion as the length of the wire is reduced. In addition, the number of winding of the coil to the length of the wire is increased, so that a magnetic flux density of a magnetic field, i.e., a magnetic force generated by the coil is increased in proportion as the number of winding of the coil is increased. Thus, the present damping actuator is capable of generating a large magnetic axial driving force and a resultant sufficiently increased oscillating force.
Further, the damping actuator constructed according to the present mode (1) of the invention, the permanent magnet is fixed to the outer sleeve member, while the permanent magnet is conventionally fixed to the inner shaft member. In this arrangement, the diameters of the permanent magnet and the outer yoke are made large, thus ensuring large circumferential lengths of the permanent magnet and the outer yoke. The large circumferential lengths of the permanent magnet and the outer yoke make it possible to obtain sufficiently large cross sectional area of the permanent magnet and the outer yoke in a cross section perpendicular to the axial direction of the inner shaft member, that is, a sufficiently large overall cross sectional area of a magnetic path, without increasing the wall thickness of the permanent magnet and the outer yoke. This means that the present damping actuator is able to generate a sufficiently large magnetic axial driving force with a sufficiently large cross sectional area of the magnetic path, while ensuring a reduced size thereof with reduced radial wall-thickness of the permanent magnet and the outer yoke.
In the present mode (1) of the invention, the inner shaft member and the outer sleeve member are preferably made of rigid materials so that the inner shaft member and the outer sleeve member constitutes an oscillating force transmitting path. For instance, the inner shaft member and the outer sleeve member made of metallic materials such as steel, an aluminum alloy or the like, are suitably used. The inner and outer yoke members are preferably made of a ferro magnetic material having a high permeability, e.g., soft iron. For instance, a material exhibiting a low magnetic hysteresis is suitably selected for the inner and outer yoke member. The permanent magnet may consist of either a single cylindrical member continuously extending over its circumference or a plurality of arcuate or curved plate-like members arranged in the circumferential direction. The permanent magnet may be suitably selected, in the light of a position or a shape of the permanent magnet, from various kinds of permanent magnets, e.g., a permanent magnet magnetized to have opposite magnetic poles at its axially opposite end faces and a permanent magnet magnetized to have opposite magnetic poles at its opposite surfaces in a radial direction perpendicular to the axial direction, i.e., at a radially inner and outer circumferential surfaces. At least one coil and at least one permanent magnet essentially need, so as to give effective magnetic poles to the inner magnetic pole portions and the outer magnetic pole portions, respectively. The numbers of the coil and the permanent magnet may be desirably increased without a specific limitation.
The inner magnetic pole portions and the outer magnetic pole portions are suitably arranged in the axial direction so that an overall magnetic force, i.e., a magnetic attractive force and a magnetic repellent force acting between the inner magnetic pole portions and the outer magnetic pole portions provides as an axial driving force between the inner shaft member and the outer shaft member, thereby causing an relative axial movement thereof. To generate the axial driving force, at least one of the inner magnetic pole portions and the corresponding outer magnetic pole portion, which are opposed to each other in the radial direction, are arranged such that an axially center portion of the inner magnetic pole portion is offset from an axially center portion of the outer magnetic pole portion in the axial direction. Preferably, all of the inner and outer magnetic pole portions, which are opposed to each other in the radial direction, have the axially center portions which are offset from each other in the axial direction.
(2) A damping actuator according to the above-indicated mode (1), wherein said permanent magnet has a magnetic pole N at one of an inner and an outer circumferential surface thereof and a magnetic pole S at an other one of the inner and outer circumferential surfaces thereof.
In the damping actuator constructed according to the above-indicated mode (2) of the invention, the permanent magnet has a sufficiently large area in cross section perpendicular to a direction in which the magnetic poles N and S are opposed to each other, while having a wall-thickness which is minimized in the direction in which the magnetic poles N and S are opposed to each other, thus reducing an overall volume or size of the permanent magnet. Further, the thus arranged permanent magnet may be used to form one outer magnetic pole portion by utilizing one of the opposite magnetic poles N and S thereof.
(3) A damping actuator according to the above-indicated mode (1) or (2), wherein at least one of the outer magnetic pole portions is located in axially intermediate position between the inner magnetic pole portions located in axially opposite sides of the coil and is given one of opposite magnetic poles N and S, and the other of the outer magnetic pole portions are opposed in the radial direction to and offset in the axial direction from the inner magnetic pole portions, respectively, and are given the other of opposite magnetic poles N and S, while the coil is in the non-energized state.
In the above-indicated mode (3), since the two inner magnetic pole portions and the three outer magnetic pole portions which are positioned relative to each other in the axial direction in the non-energized state of the coil, as described above, magnetic forces acting between these inner and outer magnetic pole portions provide respective axial driving forces in the same axial direction, when the coil is energized in one direction. Therefore, the damping actuator according to this mode (3) is capable of generating with high efficiency a sufficiently large axial driving or oscillating force between the inner shaft member and the outer sleeve member.
(4) A damping actuator according to any one of the above-indicated modes (1)-(3), wherein the coil comprises a plurality of coils which are spaced apart from each other in said axial direction of said inner shaft member with a predetermined axial spacing therebetween.
In the damping actuator constructed according to the above mode (4), a plurality of sets of the inner yoke disposed on the axially opposite sides of the coil and the outer yoke disposed so as to correspond to the inner yoke are arranged in the axial direction. That is, the present damping actuator can generate a significantly large oscillating force corresponding to a sum of magnetic forces generated by the respective sets of inner and outer yokes, thus ensuring an increased oscillating force without enlarging an outer diameter of the outer sleeve member. All or some of the plurality of coils may possibly be operable by using a common power supply controller and a common feeder circuit. Further, all or some of the plurality of coils may share the outer yoke in a single form. In this case, all or some of the plurality of coils may share the permanent magnet in a single form.
(5) A damping actuator according to the above-indicated mode (4), wherein the outer yoke is disposed radially outwardly of the plurality of coils so as to extend in the axial direction over at least two of the plurality of coils, the outer yoke having two outer magnetic pole portions which are given respective magnetic poles N and S and opposed in the radial direction to the at least two of the plurality of coils, respectively, each of the two outer magnetic pole portions being located in an axially intermediate portion between the inner magnetic pole portions located in the axially opposite side of a corresponding one of the at least two of the plurality of coils, while the coil is the non-energized state.
In the above-indicated mode (5), the damping actuator is capable of effectively generating the oscillating force acting between the inner shaft member and the outer sleeve member in the axial direction, while reducing the number of the outer magnetic pole portions. Further, the plurality of coils share the single outer yoke, leading to a simple structure of the outer yoke and a share use of the single permanent magnet with the plurality of coils.
(6) A damping actuator according to any one of the above-indicated modes (1)-(5), wherein the inner shaft member is formed with a bore extending in the axial direction thereof for accommodating a lead wire through which an electric current is applied to the coil.
In the damping actuator according to the above-indicated mode (6), the bore of the inner shaft member is effectively utilized for accommodating the lead wire, and the lead wire is effectively spaced apart from the other components which are disposed on the sides of inner shaft member and the outer sleeve member and moved relative to each other in the axial direction. Therefore, the presence of the lead wire never interrupts the axial movement of the components, leading to a high-stabilized operation of the damping actuator.
(7) A damping actuator according to any one of the above-indicated modes (1)-(6), further comprising a guide mechanism interposed between the inner shaft member and the outer sleeve member so as to permit a relative axial movement of the inner shaft member and the outer sleeve member while preventing a relative radial movement thereof. The provision of this guide mechanism stabilizes the axial relative movement of the inner shaft member and the outer sleeve member, whereby the damping actuator can generate the oscillating force with stabilized output characteristics. The guide mechanism may be a rubber elastic body or a leaf spring made of metal or a synthetic resin material, which serves to elastically connect the inner shaft member and the outer sleeve member while allowing the axial relative movement of the inner shaft member and the outer sleeve member. Alternatively, the guide mechanism may comprise: a guide pin fixed to one of the inner shaft member and the outer sleeve member so as to protrude therefrom; and a guide sleeve or bushing fixed to the other of the inner shaft member and the outer sleeve member and adapted to slidably movably receive the guide pin so that the guide pin is reciprocally movable in a desirable axial direction.
(8) An active damping oscillator, which is interposed between a vibration-source-side member and a subject member whose vibration to be damped that are connected to each other to form a vibration system, and which is adapted to apply an oscillating force to the subject member, the oscillator comprising: a damping actuator defined in any one of the above modes (1)-(7), the inner shaft member being fixed to one of the vibration-source-side member and the subject member, and the outer sleeve member being fixed to an other one of the vibration-source-side member and the subject member.
(9) An active vibration damping device interposed between a vibration-source-side member and a subject member whose vibration to be damped that are connected to each other to form a vibration system, the vibration damping device comprising: a first mounting member fixed to one of the vibration-source side member and the subject member; a second mounting member fixed to an other one of the vibration-source side member and the subject member; an elastic body elastically connecting the first and second mounting members; a damping actuator defined in any one of the above-indicated modes (1)-(7) adapted to generate an oscillating force between the inner shaft member and the outer sleeve member thereof and apply the oscillating force between the first and second mounting members.
(10) An active vibration damping device according to the above-indicated mode (9), further comprising: a primly fluid chamber partially defined by the elastic body and filled with a non-compressible fluid; an oscillating member partially defining the primary fluid chamber and being oscillated by the damping actuator so as to generate a pressure change of the non-compressible fluid in the primary fluid chamber, the pressure change of the non-compressible fluid in the primary fluid chamber acting as an oscillating force between the first and second mounting members. (11) An active vibration damper fixed to a subject member for damping vibrations of the subject member, the damper comprising: an damper actuator defined in any one of the above-indicated modes (1)-(7); an elastic member elastically connecting the inner shaft member and the outer sleeve member of the damper actuator; and a mass member fixed to one of the inner shaft member and the outer sleeve member, an other one of the inner shaft member and the outer sleeve member being fixed to the subject member.
In the active vibration damper constructed according to the above-indicated mode (11), the mass member is elastically supported by the subject member via the elastic member. That is, the mass member and the elastic member cooperate to form a vibration system. Upon energization of the coil, the oscillating force generated by the damping actuator is applied to the mass member and then transmitted via the vibration system to the subject member with excellent efficiency. Thus, the present active vibration damper is capable of exhibiting a high active damping effect with respect to the subject member.
As is understood from the foregoing description, the damping actuator constructed according to the present invention, as well as the active vibration damping device and the active vibration damper which are equipped with the damping actuator of the present invention, are all capable of generating a sufficiently large oscillating force while ensuring high power consumption efficiency and sufficient reduction in the size and weight thereof.